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I have two Bimmers - both MY 2007. The X3 3.0si (LCI) is new (to me) and I have had the 530 from new. The sound quality of the stereo in the 530 has never been very good. When I first listened to the radio in the X3 during a test drive, I was pleasantly surprised. I figured it had some premium sound package, but since actually purchasing the X3 and running the VIN numbers through BMWVIN.COM, I now realize that the two cars have identical options for the radio and speaker systems:
Code:
S645A - BMW US Radio
S676A - HiFi speaker system

However, in addition the X3 has another item in this area:
Code:
S662A - Radio BMW Business CD
I assume this simply puts a CD player in this no-navigation car.

The richer sound from the X3 seems to emanate from the under seat woofers. I hear nothing coming from the woofers in the 530 and even went as far as to physically check to see that I in fact had speakers there (I do).

I would love to hear if anyone can explain the very noticeable difference in the sound quality or if anyone has any coding ideas of how to improve the 530's sound.
(Cross posting this in E83, E60 and coding sub-forums)